Glossary

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Perceptual Learning(also: Visual Perceptual Learning, PL)

A long-studied phenomenon in vision science in which repeated exposure to, or training on, specific perceptual features — color, orientation, spatial location, shape — produces durable improvements in a person’s ability to detect and discriminate those features. Perceptual…

Perceptual Span(also: Reading Span, Visual Span)

The area of text around a fixation point from which useful information can be extracted during reading. Research using eye-tracking has shown that skilled deaf readers have a larger perceptual span than hearing readers — up to 18 letter spaces compared to 14 for hearing readers…

Peripheral Awareness(also: Peripheral Perception, Ambient Awareness)

The innate ability to unconsciously maintain and constantly update a sense of one's social and physical surroundings without actively directing attention to them. In accessibility contexts, peripheral awareness is critical for social interaction, as sighted people effortlessly…

Phantom Sensation(also: Phantom Vibration, Vibrotactile Illusion)

A phantom sensation is a perceptual illusion in which two vibrotactile actuators stimulating the skin simultaneously create the feeling of a single vibration at a point between them. By varying the amplitude and frequency of each actuator, the perceived location of the phantom…

Point-of-Gaze(also: POG, Gaze Point, Point of Regard)

Point-of-gaze is the location on a display, scene, or object at which a user's eye is currently fixating, typically reported by an eye tracker as a stream of (x, y) screen coordinates sampled at rates between 30 and several hundred hertz. Raw point-of-gaze data is noisy and…

Presence(also: Virtual Presence, Sense of Presence)

The subjective sense of being in a virtual environment, often described as the feeling of "being there" rather than simply observing a digital display. Presence is a central construct in VR research and is influenced by sensory fidelity, interaction naturalness, avatar…

Proprioception(also: Proprioceptive Sense, Body Position Sense)

The body's ability to sense its own position, movement, and orientation in space without relying on vision. Proprioceptive information comes from sensory receptors in muscles, tendons, and joints that detect stretch, tension, and pressure. For people who are blind or have low…

Pseudo-Attraction Force

A haptic illusion technique that creates the sensation of being pulled or pushed in a specific direction by exploiting the nonlinear relationship between physical and perceived acceleration. The technique uses asymmetric oscillation: a strong, brief acceleration in the intended…

Psychophysics

Psychophysics is the scientific study of the quantitative relationship between physical stimuli and the sensations and perceptions they produce. Founded in the 19th century, it uses rigorous experimental methods to measure how humans detect, discriminate, and scale sensory…

Saccade(also: Saccadic Eye Movement)

A rapid, ballistic eye movement that shifts the point of gaze from one fixation location to another. Saccades typically last 20 to 200 milliseconds, and visual processing is largely suppressed during these movements. In accessibility and eye-tracking research, saccade patterns…

Semantic Listening

A mode of listening, identified by composer and theorist Pierre Schaeffer, in which the listener focuses on decoding a coded audio signal to arrive at its intended message — for example, understanding a musical motif as representing a particular region or culture. Semantic…

Sensorimotor(also: Sensorimotor System, Sensorimotor Control)

Relating to the integration of sensory input (proprioception, vision, touch) with motor output (muscle activation and coordinated movement). Sensorimotor processes let people plan, execute, and correct movements in real time, usually without conscious effort. Neurological and…

Sensory Adaptation(also: Habituation, Olfactory Fatigue)

Sensory adaptation is the diminishing response of a sensory system to a constant or repeated stimulus over time. Classic examples include no longer noticing a steady smell, becoming accustomed to ambient noise, or losing awareness of clothing pressed against the skin. In…

Sensory Compensation(also: Cross-Modal Plasticity, Sensory Substitution)

The phenomenon whereby the loss of one sense leads to enhanced abilities in remaining senses, driven by neuro-plasticity — the brain's capacity to reorganise its neural pathways. Research shows that blind individuals, particularly those blind from birth or early childhood,…

Sensory Processing(also: Sensory Integration, Sensory Processing Differences)

Sensory processing refers to the way the nervous system receives, organizes, and responds to sensory input from the environment, including sound, light, touch, smell, taste, and movement. When sensory processing works differently — as is common in autistic individuals and people…

Sensory Saltation(also: Cutaneous Rabbit Effect, Tactile Saltation)

A perceptual phenomenon in which a series of rapid taps delivered at discrete locations on the skin are perceived as a continuous movement or hopping sensation across the surface between the tap points. In assistive technology, sensory saltation is exploited in haptic interfaces…

Sensory substitution(also: Cross-modal substitution, Sensory Substitution Device, SSD)

The technique of conveying information normally received through one sense via a different sensory channel, such as converting audio cues into vibrotactile feedback or visual signals. Sensory substitution is a foundational concept in assistive technology, enabling people who are…

Simulator Sickness(also: VR Sickness, Cybersickness, Motion Sickness in VR)

A form of motion sickness experienced in virtual reality caused by a mismatch between visual perception of movement and the vestibular system's sense of physical motion. Symptoms include nausea, dizziness, disorientation, and eye strain. Simulator sickness can be triggered by…

Simultaneous Color Contrast(also: Simultaneous Contrast)

A perceptual phenomenon where the appearance of a colour is influenced by the colours surrounding it, causing the same colour to look different when placed against different backgrounds. For example, a grey square appears lighter against a dark background and darker against a…

Situational Visual Impairment(also: SVI, Situational Visual Impairments)

A temporary reduction in a person's effective vision or reading performance caused by the environment or context rather than by a medical condition. Common examples include trying to read a phone screen in bright sunlight, while walking or on a moving vehicle, in low light, or…

Skilled Vision(also: Vernacular Vision, Professional Vision)

Skilled vision is a concept from visual culture and anthropology that describes the process of learning to see and interpret visual information in specialized ways within a particular community of practice. Originally applied to professional fields (e.g., radiologists learning…

Sound Awareness(also: Sound Awareness Technology, Environmental Sound Awareness)

The ability to perceive, identify, and respond to sounds in one's environment, and the assistive technologies designed to support this ability for Deaf and hard of hearing individuals. Sound awareness encompasses both safety-critical sounds (fire alarms, sirens, approaching…

Sound localization(also: Auditory localization, Spatial hearing)

The ability to identify the direction and distance of a sound source, relying on cues such as interaural time differences, intensity differences, and spectral filtering by the outer ear. Sound localization is critical for spatial awareness, safety, and immersive experiences in…

Spatial Reasoning

The cognitive process of understanding where objects are, how they are oriented, and how they relate to each other in three-dimensional space. Spatial reasoning is central to tasks like assembling products, navigating environments, reading diagrams, and manipulating tools. Blind…

Spatiotemporal Saliency(also: Spatiotemporal Saliency Estimation, Spatio-Temporal Saliency)

A computer vision technique that estimates, for each pixel in a video, how visually important it is at a given moment by combining spatial contrast (features that stand out within a frame) with temporal contrast (regions that change or move differently from their recent…

Speech Reading(also: Lip Reading, Lipreading, Visual Speech Perception)

The practice of understanding speech by visually interpreting a speaker's lip movements, facial expressions, gestures, and body language. Speech reading is used by many Deaf and Hard-of-Hearing individuals as a communication strategy, often in combination with residual hearing…

Speechreading(also: Lipreading, Lip Reading)

A communication method that relies on observing visual and contextual cues, primarily the movements of a speakers lips, face, and body, to understand spoken language. Speechreading is used by many d/Deaf and hard of hearing individuals as a supplement to other communication…

Subitizing

The rapid, accurate perception of the number of items in a small group without counting, typically for quantities up to about four or five. Subitizing is considered a core numerical ability that contributes to number sense development. Individuals with dyscalculia often have…

Synaesthesia(also: Synesthesia)

Synaesthesia is a perceptual phenomenon in which a stimulus in one sensory modality automatically and involuntarily triggers an additional experience in a different modality or sub-modality - for example, seeing specific colours when hearing musical notes (chromesthesia),…

Tactile Accuracy

Tactile accuracy is an evaluation criterion for measuring how well a person perceives the shape information of an object in a tactile image through touch. Unlike "naming accuracy" (whether someone can name the object), tactile accuracy captures whether the person has obtained…

Tactile Acuity(also: Touch Acuity, Tactile Resolution)

The ability to perceive and discriminate fine spatial details through the sense of touch, analogous to visual acuity for sight. Tactile acuity varies across body regions, with fingertips having the highest resolution at approximately 1-2mm spacing. In the context of…

Tactile Exploration Strategy(also: Haptic Exploration Strategy, Touch Exploration Pattern)

A systematic approach or pattern that a person uses when exploring tactile graphics, maps, or other touch-based representations. Research has identified several distinct strategies: "following outlines" (tracing the borders of shapes), "saccade" (jumping between specific zones),…

Tactile Perception(also: Cutaneous Perception, Touch Perception)

Tactile perception is the process of perceiving and interpreting information through the sense of touch, encompassing both cutaneous perception (sensing through the skin in a stationary process, detecting texture, pressure, vibration, temperature, and pain) and haptic perception…

Tactile Texture(also: Haptic Texture)

The surface quality of a material or graphic element as perceived through touch, characterized by properties such as roughness, smoothness, density, height, pattern regularity, and directionality. In tactile graphics, different textures are used to represent different regions or…

Telepresence

The extent to which a user feels present in a remote or virtual environment rather than their actual physical location. In VR contexts, telepresence describes the sensation of being transported to the virtual world. For disabled users, VR telepresence offers unique opportunities…

Texture Differentiation(also: Tactile Discrimination)

The ability to perceive and distinguish between different textures through touch. In the context of tactile graphics, texture differentiation is the fundamental perceptual capacity that allows readers to identify different regions and understand the information encoded in a…

Texture Perception(also: Texture sense, Tactile texture perception)

The perceptual capacity to detect and characterize surface properties — roughness, smoothness, bumpiness, graininess, stickiness, and directional patterns — through touch, vision, or cross-modal integration. Texture perception draws on multiple tactile channels including…

Two-Point Discrimination(also: Spatial Acuity, Tactile Acuity)

A measure of tactile sensitivity indicating the minimum distance at which two distinct points of contact on the skin can be perceived as separate rather than as a single point. Lower values indicate higher sensitivity. The fingertips have the highest two-point discrimination…

Unity Assumption

A concept from multisensory-perception research (Welch and Warren, 1980; Welch, 1999) describing the observer's implicit judgement that signals arriving through different senses originate from the same underlying event or object. When the unity assumption holds, the brain fuses…

Virtual Texture(also: Simulated Texture, Haptic Texture)

A virtual texture is a computer-generated tactile surface property rendered through a haptic device, simulating the feel of roughness, smoothness, or other surface characteristics without a physical material being present. Virtual textures are created by varying the resistance,…

Vista Space(also: Vista)

In Montello's classification of psychological spaces, a Vista is a far-field space that can be visually apprehended from a single vantage point without appreciable locomotion - a horizon view, a city skyline, a mountain panorama. Vista spaces matter to accessibility because they…

Visual Cognition(also: Visual Processing, Visual Perception)

The set of mental processes involved in perceiving, interpreting, and responding to visual information, including object recognition, spatial awareness, motion detection, and visual attention allocation. Deaf and hard-of-hearing individuals demonstrate heightened visual…

Visual Crowding(also: Crowding)

A perceptual phenomenon in which the presence of nearby flanking characters or objects makes it harder to recognise a target character, especially in peripheral vision or when the target is small, low-contrast, or briefly viewed. Crowding jointly with limited visual span sets an…

Weber's Law(also: Weber Ratio, Weber's Ratio, Weber-Fechner Law)

Weber's Law is a foundational principle of psychophysics stating that the smallest detectable change in a stimulus — the just-noticeable difference — is a roughly constant fraction of the stimulus magnitude rather than a fixed absolute amount. For example, if a user can reliably…